Recently I was working on my indexed grep. Now it could be used with Boost library, as alternative to POSIX. There are build for Windows in the release page. This version could have issues when grepping file with lines longer than 16 kB due to my simplified implementation of getline. I will probably replace it with Boost code, eventually.

There is also significant performance improvement of index generation (gripgen). Now reading file names is not blocking indexer. Also memory organisation was changed to play nicer with cache. As a result indexing over SSD drive is several times faster. Unfortunately, mechanical drive is usually the bottleneck itself, so it will be not much difference. Lower CPU load maybe. And under Windows indexing is painfully slow due to Windows Defender (at least during my test on Windows 10). It looks like Defender is scanning every file that I am opening for indexing. Excluding binary files might help, I guess.

And since file list is read asynchronously, now I could print pretty percentage progress. Of course gripgen can do it after it reads entire list, thus feeding it with find will not show you percentages until find ends.

I was also cleaning up the code, refactoring build system and adding unit tests. Further changes will be mainly polishing and bug fixing, I think. Or not, if I’ll have some great feature idea. We will see.

It is grep-like file searcher, but unlike grep, it uses index to speed up the search. We need to generate index database first, and then we could grep super fast. Instruction is on the github site, here I would like to share some notes about implementation details and performance.

How it works

This project consist of two commands: gripgen and grip. First one is used to create index database for provided file list (e.g. using external tool like find), second one search for pattern in this database.

Database is based on trigram model (Google is also using this in some projects). Basically it stores every 3-character sequences that appear in the file matched with its path. E.g. world turtle consist of trigrams: tur, urt, rtl and tle. Index format is optimised to fast lookup every file that contains given trigram. To find given pattern, grip will generate every trigram that is part of this pattern and try to find files containing every one of them. It is worth noting that this technique would generate certain amount of false positives. Index database does not contain information about order of trigrams in file, thus grip must read selected files to confirm match. This step could be disabled with the –list switch.

Because gripgen need to be supplied with file list to process, I am using find to prepare such list on the fly. Gripgen is unable to scan files itself by design. This decision vastly simplified its code base, and the many configurable switches of find results in great flexibility of these two tools combined.

As we can see here, command that produce fewer results will execute faster (sctp_sha1_process_a_block vs class). It is expected – fewer files must be read. There is also noticeable slowdown in case-insensitive search, as more trigrams is looked up in index (every possible case permutation of pattern).

Next test was performed on laptop with Intel Core i7 L620 (first generation i7) with fast SSD HDD. I’ve scanned several smaller open source projects.

This time CPU speed was the limiting factor – one core was used at 100% during the scan. I’d like to repeat this test on machine with fast CPU and SSD, but unfortunately I have no access to such device.

In both tests database size was about 10% of indexed files size. This ratio should be proportional to the entropy of indexed files. More entropy means more different trigrams to store. For typical source code tree it is expected to retain this level.

Order of magnitude smaller database with SSD drive results in way faster search. Last case insensitive query was faster than case sensitive probably because files used in previous test was buffered by the system.

Measured times are very promising – instead of wasting long minutes with grep, we could have results in mere seconds (or even in fraction of second), waiting time needed for classic grep only once – for index creation. Of course this approach is not immediately applicable to every situation, but I hope to provide useful tool for its job.

Part 1: whats broken

Maya U5 is an USB sound card with 5.1 channels support. It has pretty decent sound quality to price ratio. I bought one to use it with my Windows computer. And under Windows it works great.

Then, one day I tried to use it under Linux. As you probably guessed – it didn’t went well. System recognized this device as stereo card, sound went down randomly, volume control was not always working. Audiotrak supports only Windows and OSX, but since this is standard USB audio device it should run under everything.

So of course I asked Google for help, and found firmware that should work. It was better – system detects proper 5.1 device. But other issues still occur.

My second step was to check official website for newer firmware updates. Well, there is one. Great! Well, actually not that great. My system tells me again that I have only two audio channels. Going back to previous firmware. Except firmware flasher attached with older firmware won’t flash my updated card.

Ok, lets compare this two firmware archives. It looks like only four files is changed: flasher exe and dll, VIAFwUpd.ini and one of the bin files. I bet it is the firmware itself. But lets check the ini first.

Yeah, more errors (this error is repeated 7 times for every Audio/MIDI endpoint).

Since I have never done anything more complex with USB descriptors than looking at lsusb output, at this point I had to read a lot. There is official USB documentation here, there are also more approachable descriptions like this and that. Anyway, after some heavy reading I was able to confirm that some descriptors were broken. Probably the mixer descriptor was the problem. There is some kind of array that should map inputs to outputs, but it is truncated. Truncated MIDI descriptors also could make some trouble, but since I rarely play any MIDI, it is not priority for me.

Ok, lets look inside the device. There is VIA Vinyl™ VT2021 codec and VIA VT1728A CPU. It is hard to find anything about this chip more that it is 8032 MCU. Which is something like 8051 with extra peripherals. But wait, there is something similar. VT1620A looks like older brother of this chip. Maybe it is not full spec PDF, but it is some starting point. And IDA handle 8032 assembly.

Part 2: lets fix it

USB configuration descriptor followed by other descriptors could be found at offset 0x15ec (in firmware image release F). My first attempt was to erase MIDI endpoints. Unfortunately, this bricked the box. Flasher stopped to recognise the device.

After second examination of the board, I found 8-pin IC labelled as 25VF512A. An 512 kbit SPI flash. But how to program it without proper hardware? Well, isn’t my Raspberry PI has SPI interface? After quick googling, I’ve found Flashrom. I’ve soldered 5 wires, connected them with Raspberry and was able to resurrect Maya. Back to square one.

Having working solution to unbrick the device, we could make some more intrusive (and complicated) modifications. Ideally it would be to fix every broken descriptor. To do that, we need more room than we have (some descriptors are truncated). So we need to relocate them. But where?

I dumped whole content of flash with my Raspberry. It has 64 kB, but only about 30 kB is used by the image. Rest of the space is empty. So at the end of data, there is plenty of room.

Next we need to find references to this data. 0x15ec could be found only at offset 0x1902. It is not code, and at this moment I couldn’t figure out how it is used, but since we have working backup plan, we are safe. I’ve copied descriptors at the end of image (offset 0x78a0) updated value at 0x1902 to point to the new location and zeroed descriptors data at original location. After flashing (with Audiotrak flasher) it worked!

After many tries I was able to fix mixer and MIDI endpoints. I’ve removed remote-wakeup attribute from configuration descriptor to prevent system from suspending it. Now it is usable under Linux, but still there are minor glitches. I’ve tried to fix also newest image, but could’t make 5.1 to work, so I’ve stayed with older one.

Here is modified (fixed) firmware with new loader, so it could be flashed even on devices with newer firmware.

Vimview is my new pet project. The goal was to follow source code in vim, when using gdb. I wanted it to be done without heavy vim scripting. So I wrote a single file gdb plugin in Python. It makes vim to follow gdb frame (by opening files and moving cursor to the corresponding lines) while vim and gdb are running in separate terminals.

Vim has the ability to be controlled by RPC, gdb can be scripted in Python. That’s all what we need. Plugin and instruction are on my github.

Yes, we finally got sane, configurable mouse support. In version 2.1 they changed mouse-mode, mouse-select-window/pane etc with single mouse switch. Mouse actions now generates key events that can be mapped as ordinary keys.

In my distro (Ubuntu 14.04) there is version 1.8 of tmux, so we need to get latest from sources:

In manual (man tmux) in paragraph MOUSE SUPPORT we could read that new key events available are named MouseUpX, MouseDownX and MouseDragX where X is button no (1-3), followed by location suffix that describe where you are pointing cursor (Pane, Border or Status). So when you right-click on the status line, events MouseDown3Status and MouseUp3Status will be emitted.

Ok, but how is that better than the former method? You could now define your mouse behaviour as you like. That include (some limited) use of scripting. E.g. to spawn new window after selected by right click on the status line label, you could add something like this to your .tmux.rc:

Option -t= means that the target is window/panel (depends on command) that is clicked.

Or maybe you want to be able to reorder windows in status bar by drag & drop?

bind-key -n MouseDrag1Status swap-window -t=

Ok, that’s great, but we all know what you really want in tmux.

Scroll with mouse in every situation

Yep, it is possible with tmux 2.1. It is not pretty, but it works. And by every situation I mean normal and alternative terminal mode and also tmux copy mode (when you can scroll through history). You could even scroll up to access this mode.

Command if-shell -F is used to check given variable value. If it is non-zero and non empty, first argument will be evaluated, otherwise, second one. Flag pane_in_mode is set if pane is in tmux copy mode. mouse_button_flag is set when running app is actively capturing mouse (like vim). alternate_on is set whenever terminal working in alternate mode (where there is no history to scroll by, like top). If you want to debug these variables, you could print them in status line

Construction like #{?pane_in_mode,1,#{mouse_button_flag}} checks the value of first variable and returns 1 if it is non-zero, second variable value otherwise. It is logical OR constructed with if-shell syntax.

Starting from second example – wheel down. If we are in tmux copy mode or running app want to catch mouse, we send mouse escape strings directly (send-keys -M will pass through mouse events). Otherwise we are sending down arrow key three times. Why not pass mouse event in all cases? Well, if running app don’t tell terminal to catch mouse, most terminals will be doing same thing. That’s why you could scroll through less and man pages.

Wheel up scenario has one more condition added. You can go to copy mode, and then scroll through tmux history when you are not in alternative mode.

This is most sane setup that I’ve been able to come with. It works with shells, vim, man pages, less, htop, mc without breaking terribly anything. One drawback (for me) is, scrolling through tmux copy mode progress by one line at a time. It probably could be fixed by adding extra condition to these lines, but I’m afraid that it will break something. And it is obfuscated enough, already.

There are some kernels for this NAS on theweb (binaries and configs), but everything I could find was super old (like kernel 3.6.9 old). Because I’ve been able to successfully build current longterm version of Linus tree kernel, here is me sharing my solution.

It is based on this instruction. The kirkwood_defconfig was merged with mvebu_v5_defconfig so we are using the second one instead. I’ve pushed my config, patches and cross-compilation script to my github: https://github.com/sc0ty/nsa310-kernel. There is everything explained in README.md, I won’t repeat myself here. I’ll try to keep this repository up to date with Linus kernel as long as I am using this NAS myself.

I’ve started using f.lux some time ago and now I cannot live without it. But there is one disadvantage considering my use case. Whenever I want to see a movie (which is usually at evening when f.lux is making everything reddish) I have to disable it manually. Through context menu. Because hotkey allows you to disable it only for one hour. And my movies usually are longer than that. So what can I do? Fire an IDA, of course.

Where to start? I’ve tried to find string that is shown after pressing these keys (ALT + END): “for an hour” and “f.lux is back”. Strings window found it at address 0x483850 and 0x483860 (f.lux v. 3.10 for Windows). IDA could find only one reference to these addresses in single function sub_458330. Great, lets put breakpoint at the beginning of this function and lets see what happen.

Breakpoint will hit frequently after the program starts. It must be some kind of message processor. Ok, lets put breakpoints on lines referenced to strings (0x4585D6 and 0x4585E2 – see picture on the left) instead of begginig of function. Now we can see that it hits only on hotkeys, but not on menu click. Great.

Looking around this place we could find an interesting value. At address 0x4585B9 there is label pointing to double float:

.rdata:00490240 dbl_490240 dq 3600.0

3600 which is number of seconds in hour. Coincidence? And what is this strange fld instruction? Probably some mov with float argument. Lets find it.

I’m not sure but it looks like this value is placed on the stack as argument to sub_452BD0 function. Lets break on this function and try to modify the value on the stack. I found online float to binary converter here http://babbage.cs.qc.cuny.edu/IEEE-754.old/Decimal.html. I’ve tried to change this to 10 secs, which is 0x4024000000000000 (use double precision). It works, so all we need to do is to patch executable with value corresponding to 3 hour time or so and maybe change strings accordingly, right?

Why not “disable until sunrise”?

Why not just remap ALT + END to call this function? It has no shortcut whatsoever. Lets find this string. It is used at address 0x457DD0 as parameter to AppendMenuA function. But it is here registered, not executed. Maybe we should try different approach: lets find xrefs to sub_452BD0. We should find proper message processor associated with menu this way.

There is five of them. Lets break on four yet unexamined. This way we will detect the one called by menu. As we can see, it is 0x457FCF. But wait, there is similar code next to it.

Only difference is in timeout parameter passed to our function – it is -1 this time. Is it some special value to indicate this “until sunrise” mode? Lets find out. We already have breakpoint in here, so we only have to click this option from menu. And it breaks!

Finally our hack comes to modify this single value at address 0x4585B9 (hotkey handling function). Or I suggest to modify instruction to load value -1 from address 0x4901F8 instead to not affect other places where this value is used (and there is several such places). And maybe changing string “for an hour”.

Oh wait, “until sunrise” is too long to fit in there! What now?

Don’t worry, there are at least two possible solutions. We could use another string here. “Until sunrise” is presented at 0x483888. And if you want string that starts with lower case, you could use “Disable until sunrise” at 0x483724 but skipping the first word.

If you still couldn’t find any useful string, you could always add new one. At the end of .rdata section there is more than 400 bytes unused. You can put your string there. Don’t forget to update virtual size of this section in section header.

Unfortunately f.lux license forbids me to publish modified version. Instead, I would present patching instruction in form that it would be easy to patch with any hex editor.

I actually never have my own station. I always have been using cheapest soldering iron without any regulator. Of course I has access to such equipment in work, but it’s not the same. And I quit that work lately.

My first attempt to improve my iron was to add a diode serially with heater. It cut out half of the supply sine, so the iron works with the half of its power. I’ve added also a switch parallel with the diode which allow me to use also the full power. That improvement let me to decease power when the bit becomes too hot.

About a week ago I decided to build a real station. I bought an iron (Solomon SL10: 24V, 48W with thermocouple). Most expensive part – transformer I already have, thanks that I’ve saved a lot of money.

Here is the schematic (click to enlarge):

P1 is where you set the temperature, with P2 you could calibrate the device. It could also display temperature using attached panel voltmeter. I’ve selected resistor values to work with digital voltmeter in range of 20.00V (0.01V correspond with 1°C). IC1A amplify voltage from thermocouple to achieve this range. Using S2 you could select which temperature you’d like to measure (real or set).

P1, R1 and R2 makes the temperature range which you could set to about 150-460°C. IC1B works as comparator, it powers up OK1 whenever the amplified voltage from thermocouple is smaller from the voltage from P1. I’ve used this optotriac instead of connecting T1 directly to cancel out the noise generating during heater powers up (MOC3041 have build-in zero detector).

Because my transformer has 2x12V output (not a single 24V) I was able to install power selector switch (S1). I could select heater voltage (12V/24V) by this switch. In practice it turns out to be very useful, especially that I have build such simple regulator without thermocouple compensation. With full power iron gains heat quickly but if I need stable temperature to solder some SMD I could switch to 12V and it is able to hold selected temperature very accurate (it changes +/- 2°C).

Only thing that I want to improve is to change the soldering iron. Solomon SL10 has termocouple too close to the heater. In result the bit temperature is significantly smaller than measured one. But what to expect from 10$ iron.

I’ve developed new version of my VSMTools (BlackBerry branding files editor/extractor). Version 0.7 is much smaller, better optimized and contains some minor fixes. From this version VSMTools will be released as open source under GPL licence. You can obtain sources from github.